The present invention relates generally to load carrying shock absorbers. More particularly, it relates to shock absorbers of the type which are mounted to vehicles and which use both an elastomeric spring and a selectively pressurizable gas chamber for carrying and leveling load, absorbing shock, and energy dissipation. However, it will be appreciated by those skilled in the art that the invention can be readily adapted for use in other environments as, for example, where similar spring dampening devices are employed to protect or cushion other items.
Known spring damper devices of the type described have included elastomeric shear springs, elastomeric diaphragms, selectively pressurizable gas chambers and associated communicating fluid chambers including restrictive orifice means therebetween for restricting the flow of fluid between the fluid chambers. Such a spring dampening device is described in Application Ser. No. 208,013, filed Nov. 18, 1980, now abandoned, in the name of Shtarkman et al and assigned to the assignee of the subject application. In the Shtarkman et al application an expandable and contractable elastomeric bladder for separating a gas chamber from a fluid chamber in a viscous spring damper is provided. Varying the pressurization of the gas chamber is employed for varying the spring rate of the viscous spring damper, calibrating the damper or leveling a load supported thereby. In addition, fluid flow between the communicating fluid chambers absorbs and dampens the shock and spring forces occurring during operation of the device. Such a structure provides the advantageous operating characteristics of both a spring and a shock absorber in one package.
A particular problem inherent in viscous spring dampers including fluid chambers is the limitation of a short stroke. In other words, the extent of compressive reduction of the spring damper device may be unduly limited because the volume of fluid that must be displaced between communicating fluid chambers may become too great to allow compressive reduction of the device to a desired level. There may simply not be enough room for the fluid, which is typically an incompressible hydraulic fluid, to be displaced. As a result, failure of the viscous spring damper would occur upon compression of the device beyond a certain level, either occurring through fracture of the device's housing or shear spring, or through shear spring bond failure.
Another problem with prior viscous spring dampers is instability of the spring characteristics upon excessive deflection of the device. Specifically, an elastomeric shear spring is stressed primarily in shear upon deflection of a viscous spring damper. However, in situations where the viscous spring damper is stroked or compressed beyond a point where the shear spring becomes unstable, the shear spring operates irregularly. On a load/deflection curve, this is manifested as a drop in load with increasing deflection, rather than a steady increase in load with increasing deflection. Once in this position, it is difficult for the spring to expand or "flip back" rapidly. Such difficulty further results in slow response in the operation of the viscous spring damper.
Yet another problem with prior viscous spring dampers is that the natural frequency of spring response is dependent upon the mass supported by the device. When employed in a vehicle suspension system, a non-constant natural frequency device translates into rider discomfort as a vehicle becomes loaded.
The present invention contemplates a new and improved dry viscous spring damper which overcomes all of the above referred to problems and others to provide a new viscous spring damper which is simple in design, economical to manufacture, readily adaptable to a plurality of load carrying and shock absorbing uses, and which provides improved shock absorption and energy dissipation.